The Depo Shot

I was on the depo shot for 13 years after having three kids .. I had no period during the whole time I was on the shot .. I got off about a year ago and started my period after 3 months off of the shot I have now been off of it for 1 year and 4 months but I only bleed for three days .. I haven't gotten pregnant yet am I supposed to be having only a 3 day period? Has this happened to someone else?